1. Technical Field
The present invention relates to a white color printed material formed by using a white ink, and more particularly relates to, besides providing a novel method for evaluating a white color shielding degree of a white color printed material printed on a transparent substrate having no ink absorbing properties, a method for manufacturing a white ink based on the white color shielding degree, a support apparatus for manufacturing a white ink, and a method for manufacturing a white color printed material.
2. Related Art
An ink jet recording method is able to record a highly fine image by a relatively simple device and has been rapidly developed in various fields. In addition, the ink jet recording method has been used in many various fields, and in accordance with each application, appropriate recording medium and/or ink is used.
In addition, as the index for evaluating a white color printed material formed by using a white ink, an L* value (degree of lightness by reflected light) has been commonly used.
In addition, heretofore, the visibility has been improved by using a white color material (pigment), such as titanium oxide. However, since the thickness of an ink layer is increased at a dot portion of a color image, curing by radiation of active energy rays through a white color layer cannot be sufficiently carried out, and hence, because of curing defects of a color ink layer, for example, color bleeding is generated.
As for a white ink, an ink jet recording method has been known which has superior visibility and gradation reproduction characteristics even when a transparent recording medium or a recording medium having low lightness is used (see JP-A-2003-182061).
The following has been disclosed in JP-A-2003-182061.
When an image is viewed on a recording medium, a white image is formed with a white ink on a recording medium using an ink jet printer having gradation reproduction means, and a color image having gradation characteristics is formed as a normal image on the white image using a color ink.
In addition, when an image is viewed through a recording medium, a color image having gradation characteristics is first formed on the recording medium as a reversed image, and a white image is then formed thereon using a white ink.
In the case described above, in order to obtain superior color development and gradation characteristics of a color image, a white ink layer having a transmission density of 0.15 or more and an L* value of 65 or more is preferable.
More preferably, the transmission density is 0.2 or more, and the L* value is 70 or more. Accordingly, when the values are lower than those described above, or when no white ink layer is present, the contrast between a recording medium and a color image cannot be obtained, and as a result, the visibility may be degraded, or in particular, since the gradation characteristics are not obtained in a low density region, degradation of image quality may occur in some cases. Although the upper limit is not particularly defined, as a level of high density in view of ink manufacturing, the transmission density is 0.5 or less, and the L* value is 100 or less.
According to the invention disclosed in JP-A-2003-182061, it has been disclosed that in order to obtain superior color development and gradation characteristics of a color image, the transmission density and the L* value are preferably set to 0.15 or more and 65 or more and more preferably set to 0.2 or more and 70 or more, respectively. Hence, in the above invention, higher transmission density and L* value are both particularly specified.
The white ink disclosed in JP-A-2003-182061 shows the restriction to obtain superior color development and gradation characteristics of a color image.
The inventor of the invention discovered that although as a related index for evaluating a white color printed material, the L* value (degree of lightness by reflected light) is generally used, shielding characteristics (shielding degrees) of white color printed materials are differently viewed in many cases even if the L* values thereof are equal to each other, and that this difference is caused by the type and the content of resin used for a white ink.